1. Field of the Invention
This invention relates to a process for preparing imidacloprid in the presence of an alkali carbonate in an organic solvent.
2. Description of the Related Art
Imidacloprid (1-[(6-Chloro-3-pyridinyl) methyl]-4,5-dihydro-N-nitro-1H-imidazol-2-amine) is known as an insecticide, and is a neonicotinoid compound, which has been disclosed in U.S. Pat. No. 4,742,060, and which has a formula as shown below: ##STR1##
Wherein n=0 or 1; X=S, O, --N--R7 or --CH--R8; Y=N or =C--R9; R7, R8, R9=hydrogen or specifical organic radicals; Z=5- or 6-membered nitrogen-containing heterocyclic ring; R1, R2, R5, R6=hydrogen or alkyl group; R3, R4=hydrogen, hydroxy group or alkyl group. The neonicotinoid compound can be synthesized by reacting a hetercyclic compound with an amine compound in the presence of an alkali base in an organic solvent.
The aforesaid alkali base can be NaH or an alkali carbonate when the amine compound employed in the reaction is a uni-amine compound. However, it is preferable to employ NaH when the amine compound employed in the reaction is a di-amine compound. The alkali carbonate is not suitable for the reaction involving the di-amine compound due to a relatively poor yield. The aforementioned reactions can be represented by the following two examples: ##STR2##
Imidacloprid can be prepared by reacting 2-nitroiminoimidazolidine (a di-amine compound) with 2-chloro-5-chloromethyl pyridine (CCMP) in the presence of 60% NaH in an organic solvent, such as DMF (diemthyl formamide), at a temperature ranging from room temperature to about 80.degree. C. However, the use of NaH would give rise to safety concerns and transport problems. Moreover, the reaction has a poor yield. It is found that when NaH is replaced by alkali carbonate in the aforementioned reaction, a relatively large amount of by product is produced. The reaction can be represented as follows: ##STR3##
Due to the aforementioned drawbacks, a two-step reaction process for preparing Imidacloprid has been proposed heretofore, which can be represented as follows: ##STR4##
While the aforesaid yield can be improved and the aforesaid safety concerns and transport problems can be overcome by using the two-step reaction, the two-step reaction process is complex and costly.